Crimping of yarn

ABSTRACT

the improvement in methods and apparatus for controlling stuffing box crimping comprising photocell measuring means arranged to provide a signal smoothly related to the amount of yarn in the buffer chamber. The ratio of withdrawal to delivery of the yarn in controlled thereby maintaining the amount of yarn in the buffer chamber constant with the counter-pressure measurement regulator maintaining the controlled ratio at a constant value.

Jan. 18, 1972 A, L A, TAMB|N| 3,636,149

CRIMPING OF YARN Filed Dec. 22, 1969 I N V E N T O R A/ffza fa/67 @fewo ,Z0/www ATTORNEY United States atent 01 3,636,149 CRIMPING F YARN Angelo Luigi Alfredo Tambini, Pontypool, England, as-

sgnor to Imperial Chemical Industries Limited, London, England Continuation-impart of application Ser. No. 718,266,

Apr. 2, 1968. This application Dec. 22, 1969, Ser.

U.S. Cl. 264-40 lut. Cl. 962g 1/12 27 Claims ABSTRACT 0F THE DISCLOSURE This is a continuation-in-part of application Ser. No. 718,266, led Apr. 2, 1968, now abandoned.

The present invention concerns improvements in or relating to the crimping of yarn by the so-called stutterbox process. In this speciication, yarn is used as the generic term to include any textile libre or filament or assemblies of fibres and filaments and is not to be read as being restricted to fibres, filaments and assemblies of any particular thickness.

The use of stutter-box crimpers in the production of crimped yarns is well known. Generally, uncrimped yarn is conveyed by delivery rollers into a stutter-box which is restricted at a suitable point by a moveable counter-pressure means, for instance a tlap or a plunger. The yarn is compressed inside the stufferbox until the internal pressure is suiiicient to force open the counter-pressure means when crimped yarn exits the stutter-box and may then advance or be advanced to subsequent operating stages, and a state of equilibrium upon which the crimping eiiect depends will be reached between the pressure exerted by the yarn and the pressure exerted by the counter-pressure means.

In practice, the crimping effect may not be constant owing to various inuences such as, for example, variations in denier, moisture content or frictional properties of the yarn fed to the crimper and it is necessary to measure regularly some crimp characterising parameter and adjust the pressure exerted by the counter pressure means if necessary to keep the crimp characteristics within limits, the limits which may be tolerated for the particular crimped yarn which is being manufactured.

A suitable and commonly used parameter for characterising crimp is that of crimp ratio which I define herein as the ratio of the length of sample the uncrimped yarn to the crimped length of such sample. The measurement of the crimp characterizing parameter generally has to be performed by hand, however, and this is a tedious process and long delays may occur before corrective action if necessary can be taken.

I have discovered a method of producing stutter-box crimped yarn having crimp characteristics (as determined by the ratio of rate of delivery of yarn to the stutter box to the rate of withdrawal of yarn therefrom) lying between small arbitrary limits without the necessity of performing tedious hand tests and accordingly the invention comprises, in one of its aspects, a method of producing stutter-box crimped yarn which comprises feeding yarn into a stutter-box crimper having adjustable counterpressure means, collecting a mass of crimped yarn from said crimper in a buffer chamber and withdrawing yarn from said butter chamber, measuring the amount of yarn in said buffer chamber by photoelectric means arranged to provide a signal substantially smoothly related to the amount of yarn in said lbutter chamber, controlling the ratio of the rate of withdrawal of yarn from said chamber to the rate of delivery of yarn to the crimper in response to said signal so as to maintain the amount of yarn in said buffer chamber substantially constant, monitoring said ratio and adjusting said counterpressure means to maintain said controlled ratio at a substantially constant value.

By the amount of yarn in the butter chamber I mean that length of the wad of crimped yarn passed from the, crimper into the buffer chamber. When the crimping effect, delivery rate and withdrawal rate are all constant, an equilibrium will be set up so that the amount of yarn in the chamber will also remain constant.

In another of its aspects the invention comprises apparatus for producing stutter box crimped yarn which comprises a stutter-box provided with adjustable counterpressure means and delivery means for feeding yarn into said stutter-box, a butler chamber situated so as to collect yarn exiting said stutter-box, photoeletcric means for measuring the amount of yarn in said chamber arranged to provide a signal substantially smoothly related to the amount of yarn in said chamber, means for Iwithdrawing the yarn from said buffer chamber and means for controlling the ratio of the rate of withdrawal of yarn from said chamber to the rate of delivery of yarn to the crimper in response to said signal as to maintain the amount of yarn in the chamber substantially constant, means for monitoring said controlled ratio and means for regulating the counter-pressure means in order to maintain said controlled ratio at a substantially constant value.

The method is based on the fact that an uncrimped length of yarn fed to the crimper is longer than its crimped length. If the yarn delivery and yarn withdrawal means are running continuously, the take-up means should therefore run more slowly than the delivery means, the ratio of the rate of delivery to the rate of withdrawal being related to the crimp ratio. If the crimping effect remains constant, the control system ensures that there is always the same amount of yarn between the crimper and the Withdrawal means. If the crimping elTect varies and if the control system is not used then the amount of yarn between the crimper and the withdrawal means will vary. If the crimp ratio decreases, yarn will build up ibetween the crimper and the withdrawal means and vice versa.

The control system of the invention will detect the variation in the amount of yarn contained between crimper and withdrawal means and will vary the ratio of rate of yarn delivery to rate of yarn withdrawal to cause the amount of yarn to remain constant. By monitoring the change in the controlled ratio it is possible to observe drifts in the crimping effect and to correct the counterpressure means to ensure that the crimping effect is maintained between limits which may be tolerated 1n the particular crimping process.

The ratio of rate of yarn delivery to rate of yarn withdrawal may be varied by variation of the rate of delivery, or by variation of `the rate of withdrawal, whilst maintaining the non-varied rate at a constant value. The choice of which rate is to be varied will be determined by the nature of subsequent or preceding processes acting on the yarn. For example, it may be desired to keep the rate of delivery constant if yarn is supplied to the crimper assembly from a spinning or drawing machine. For ease of description the following discussions will relate to systems in lwhich the rate of delivery of yarn to the crimper is constant and the withdrawal rate is controlled by the signal from the photoelectric means although it is to be understood that the scope of the invention is not limited in this way.

Thus, in one process of the present invention, under conditions of constant crimping effect, `the withdrawal rate will 'be controlled at a certain rate depending on the amount of yarn in the chamber, the amount of yarn in the chamber will remain substantially constant and the ratio of the rate of yarn delivery to the stuffer box to the rate of withdrawal of yarn from the chamber will be related to the crimp ratio. If, for instance, a decrease in the crimp ratio then occurs, yarn will commence to build up in the chamber, and the withdrawal rate will be increased by the control system.

The change in the amount of yarn in the buffer chamber will be detected so that the build-up is controlled. The ratio of yarn delivery rate to the new withdrawal rate will be related to the new crimp ratio and action can be taken if necessary to restore the original crimp ratio by suitable adjustment of the counter-pressure means after which adjustment the withdrawal rate will decrease by the action of the control mechanism, to the original value.

In practice it is impossible to withdraw the crimped yarn from the buifer chamber without imposing some tension on the crimped yarn and hence the ratio of rate of yarn delivery to rate of Withdrawal of yarn measured in the process of this invention will not generally be identical to the crimp ratio, measured by hand. I have found, however, tha-t the values bear a constant relationship to each other for particular sets of running conditions, providing that care is taken to prevent undue tension variations in the crimped yarn being delivered to the yarn withdrawal means, and hence the ratio values measured in the process of this invention can be used as a crimp characterising parameter. ldeally the path of travel of the crimped yarn from the buffer chamber to the yarn withdrawal means should be as short as possible and be as free as possible from changes of direction and contact with guides etc.

The buffer chamber should preferably have the Same cross-sectional dimensions as the stuffer box, may be of any desired length and is preferably oriented so that yarn exiting the stulfer box does not substantially change direction. The stutter box and buffer chamber should be fabricated of hard wearing material and stainless steel is preferred for its hard wearing and anti-corrosion properties.

The photoelectric means may comprise for instance, a plurality photoelectric celis arranged in the chamber and illuminating means either at the opposite side of the chamber from the photoelectric cells so that yarn can interpose between them. Alternatively, the illuminating means, in a preferred embodiment is situated, Say, at one end of the chamber so as to illuminate the chamber With diffuse light. If the latter arrangement is used, the inside of the chamber may be polished to assist in light distribution. The cells and/or the illuminating means are preferably situated inside the chamber, i.e. let into the walls of the chamber so that they may be wiped by the yarn in its passage past them, and so may be cleansed of light masking deposits, or, alternatively may be situated outside lthe chamber and able to detect the amount of yarn in the chamber through slots, holes or transparent windows.

The only limitation as to the arrangement of the photoelectric means is that it should be arranged to produce a signal substantially smoothly related to the amount of yarn in the chamber. By a substantially smoothly related signal I mean one in which for every amount of yarn in the chamber there is a unique signal produced in contradistinction to a stepped signal, for example, one in which two photo-electric cells are spaced apart and a signal of a value is produced when the amount is below the level of one photo-electric cell a signal of a diiferent value is produced when the amount is between the two photo-electric cells and a signal of a third value is produced Iwhen the amount is above the second photo-electric cell. The use of a step signal of this sort would not be useful in the process of this invention since the ratio of yarn delivery speed to yarn withdrawal speed would not be closely and continuously related to the amount of yarn within the buffer chamber.

l have found that one arrangement for achieving a signal which is substantially smoothly related to the amount of yarn in the chamber is to arrange a number of photo-electric cells, illuminated by direct or diffuse light, along the chamber each shunted with a suitable resistor to give a smooth characteristic from one cell to the next, connected in series and giving an electrical si-gnal which is suitably amplified and fed to a motor controller which controls the speed of the yarn withdrawal means. The yarn in the Chamber transmits a certain amount of light so that the intensity of light falling on the cells is not suddenly reduced by interposition of yarn, and consequently each cell is sensitive to the amount of yarn between it and the source and does not have a sharp switching action and a smooth related signal results. The number of cells required to produce a suitable signal will of course depend on the particular circuitry, the type of cell and the optical arrangement chosen. The relationship between the electrical signal and the amount of yarn in the chamber can be made to have any desired form by suitable choice of cell positions and types and shunting resistance and the overall response can be tuned to provide a smooth, preferably linear characteristic, by choice of suitable values of shunting resistances.

The delivery and/or yarn withdrawal means may conveniently be pairs of nip rolls driven by variable speed motors, although especially in the case of the withdrawal means care is necessary in choosing material for the nip rolls to prevent yarn lapping and one or both of the nip rolls may conveniently he part of a conveyor system.

The control means can comprise any means for producing any desired control signal from the signal from the photo-cells and may include conventional circuitry providing proportional control or proportional plus integral control` The feed and/ or withdrawal rate monitoring means may conveniently be speed transducers arranged to measure the speed of the nip rolls although of course any other means for measuring the rates may he used. The withdrawal rate measuring means may be linked with the means to measure the rate of yarn delivery measuring means via a rate comparator to indicate the ratio of the two rates 4of some related value, which ratio or value will, as explained above, be related to the crimp ratio of the yarn. The crimper counter-pressure may be adjusted, if necessary, according to the variation of the withdrawal rate measurement (or if measured the ratio of the rate of delivery to rate of withdrawal or related value) from its desired value by any convenient relay proportionally to the error signal, or, if necessary, by hand.

My invention will now be described, by way of a specic example, with reference to the accompanying drawing which is a schematic part-sectional View of apparatus according to the invention. The reader will understand that my invention is in no way limited to the following description and that the specific values mentioned are solely by way of example. It will also be understood that the specific values may be altered to give response characteristics which may provide a more or less critically controlled process depending on the end use of the yarn being treated.

The drawing shows a stuflier-box 11, which has a rectangular cross-section of 2 sq. in., and fabricated of stainless steel. Extending contiguously and coaxially of stutter-box 11 is buffer chamber 15, having substantially the same dimensions as stutter-box 11 and having a length of about 24". The buffer chamber 15 is also fabricated of stainless steel and the internal walls thereof are highly polished. Stuler-box 11 is provided with counter-pressure means 18 consisting of a pivoted ap in a side wall, acted upon by an air pressure cylinder and piston 19. The counter-pressure may be adjusted by adjustment of valve 20. The yarn delivery means consist of nip rolls 12 situated at the open mouth of stutter-box 11 in a conventional manner, and similarly yarn withdrawal means consists of nip rolls 16 situated at the open end of buffer chamber 15. Nip rolls 12 are driven at a constant rate of 900 ft./min. through a motor and gearbox shown generally as 13. Nip rolls 16, however, are driven through a variable speed D.C. motor and gearbox shown generally as 17. Buffer chamber 15 is provided with four photoresistive cells 21 (Type NSL 453 supplied by National Semiconductors Limited) -which havehigh resistance at low light intensities and low resistance at high light intensities situated at 2 inch intervals along chamber 15 and projecting into chamber 15, and four 6 watt bulbs 22 situated in chamber 15 at a position remote from cells 21 and at the opposite end to stutter-box 11. The use of diffuse light from bulbs 22 to illuminate cells 21 is preferred to direct light from bulbs situated diametrically opposite cells 21, since the false response from the cells caused by yarn being withdrawn from the chamber interrupting the direct illumination of the latter case is prevented. Cells 21 are shunted with 12 kilo-ohms resistors and are connected in series across a l2 volt D.C. power source. The photocell and shunt resistor assembly thus acts as a variable resistance, having a minimum resistance of about 1 kilo-ohm when light is falling on all photocells, and a maximum resistance of about 50 kilo-ohms when not illuminated. A 50 kilo-ohm resistance 25 is connected in series with the photo-cell and the voltage drop across the cell and shunt resistance assembly is thus in the range 1/2 v.-51/2 v. Transistors 27, 28 and resistors 25, 26 are connected to form a Darlington pair circuit which acts as an impedance matching device to pass the control signal from the cell and shunt resistance assembly to a standard commercially available closedloop, thyristor D.C. motor controller shown generally as 29, which receives a signal of between -5 volts depending on the response of the photocells and shunts assembly. The controller 29 adjusts the voltage applied to the variable speed motor in 17, such that when the signal is 0 volts the speed of the motor is zero, and when the signal is volts the speed of the motor in 17 is such that nip rolls 16 travel at the same rate as input nip rolls 12, namely 900 ft./min.

One small disadvantage encountered with the use of diffuse light illumination of photocells 21 is that the intensity of the illumination falling on the cell furthest from the light source is less than that falling on the cell nearest to the light source, which means that the voltage across the photocell assembly when all cells are illuminated is not the required 1/2 volt but say l-1.5 volts. This residual signal when fed via to the motor controller to the withdrawal motor means that the withdrawal means do not stop when all cells are illuminated. This problem is readily overcome by using an additional photo resistive cell 24 situated near the inlet end of chamber 15 and connected in parallel with the photo-cell-shunt assembly.

In operation an uncrimped 500 kilodenier tow, 10, composed of 12 d.p.f. nylon 6.6 continuous laments is fed at 900 ft./min. by nip rolls 12 into stuffer-box 11. Crimped tow is forced from stuffer-box 11 into butler chamber and an end is brought into contact with nip rolls 16. Buffer chamber 15, photoresistive cells 21, motor speed controller and yarn withdrawal means 16 form, a closed loop control system. The photo-resistive cells 21 detect the amount of tow in buier chamber 15 and the detector signal is fed to motor controller 29. The signal received by the motor controller is typically zero volts when buffer chamber 15 is empty and 5 Volts when buffer chamber 15 is full. The motor controller 29 is set so that the yarn withdrawal means is stationary when the control signal is zero, and equal to the speed of the yarn delivery means 12 (in this example 900 ft./min.), when the amplified signal is at its maximum value of 5 volts.

The crimp ratio of the yarn is measured manually in order to correlate crimp ratio and rate of yarn withdrawal i.e. the apparatus is calibrated and the crimp ratio is adjusted as necessary by adjusting the counter-pressure in stufer-box 11 to obtain the desired crimp ratio of 25%. Once the correct crimp ratio has been established, there is no need for further manual measurement of the value of crimp ratio, apart from a check at, say, three monthly intervals. Even if the process is halted, on recommencement the value of crimp ratio will be unchanged at the selected value. In this example the counter-pressure necessary was about 33 lbs. per sq. inch and the rate of withdrawal of crimped tow was 640 ft./min.

The speeds of the pairs of nip rolls 16 are measured by a speed transducer (not shown), the output of which is fed to a printing device 30 which prints out the speed of rolls 16 at short intervals. If the value of the ratio drifts outside the 1% tolerance limits chosen for the process, the pressure on the movable ilap 18 is adjusted by adjusting valve 20 manually, or by means of a suitable relay (not shown) so as to maintain the speed of nip rolls 16 at the value corresponding to the selected crimp ratio of 25% il%, that is the Withdrawal speed is maintained between 635-645 ft./min. Alternatively printing device 30 may be coupled with a comparator which compares the speeds of rolls 12 and 16 and prints out the ratio of the difference in speeds of rolls 16 and 12, to speed of nip rolls 12.

If the supply of uncrimped tow to the stuffer-box is interrupted, the amount of crimped yarn in the buffer will fall until it reaches the vicinity of photo-cell 24. The signal then fed to the withdrawal motor speed controller will be 0 volts and the withdrawal of yarn will cease. On recommencement of the supply the control system will operate as before to bring the withdrawal nip rolls 16 up to speed and the yarn will have al crimp ratio of 25%i1% at all points if the withdrawal rate is maintained between 635-645 ft./min.

In an alternative design photo-cells 21 are illuminated by direct light from light sources situated diametrically opposite. In this case photo-cell 24 becomes redundant.

What I claim is:

1. A method of producing stutter-box crimped yarn which comprises feeding yarn into a stutter-box crimper having adjustable counter-pressure means, collecting a mass of crimped yarn from said crimper in a buifer chamber and withdrawing yarn from said butfcr chamber, measuring the amount of yarn in said buffer chamber by photoelectric means arranged to provide a signal substantially smoothly related to the amount of yarn in said buffer chamber, controlling the ratio of the rate of withdrawal of yarn from said chamber to the rate of delivery of yarn to the crimper in response to said signal so as to maintain the amount of yarn in said buffer chamber substantially constant monitoring measuring said ratio, and adjusting said counter-pressure means to maintain said controlled ratio at a substantially constant value.

2. A method as claimed in claim 1 in which the rate of delivery of yarn to the crimper is substantially constant and the rate of withdrawal of crimped yarn from the said buffer chamber is controlled by said signal.

3. A method as claimed in claim 1 in which the rate 0 withdrawal of yarn from the said but-fer chamber is substantially constant and the rate of delivery of yarn to the crimper is controlled by ysaid signal.

4. Apparatus for producing stuffer-box crimped yarn which comprises a stulfer box provided with adjustable counter-pressure means and delivery means for feeding yarn into said stuifer-box, a buffer chamber situated so as to collect yarn exiting said stutter-box, photoelectric means for measuring the amount of yarn in said chamber arranged to provide a signal substantially smoothly related to the amount of yarn in said chamber, means for withdrawing the yarn from said butler chamber and means for controlling the ratio of the rate of withdrawal of yarn from said chamber to the rate of delivery of yarn to the crimper in response to said signal so as to maintain the amount of yam in said buffer chamber, substantially constant means for measuring said ratio and means for regulating the counter-pressure means in order to maintain said controlled ratio at a substantially constant value.

5. Apparatus as claimed in claim 4 which the delivery means operates at a substantially constant rate and the withdrawal means is controlled in response to said signal.

6. Apparatus as claimed in claim 4 in which the withdrawal means operates at a substantially constant rate and the delivery means is controlled in response to said signal.

7. Apparatus as claimed in claim 4 in which the photoelectric means comprises photo-electric cell means and illuminating means.

8. Apparatus as claimed in claim 7 in which the photoelectric cell means is housed in the walls of the chamber.

9. Apparatus as claimed in claim 8 in which the photoelectric cell means projects into the interior of the chamber.

10. Apparatus as claimed in claim 7 in which the photoelectric cell means is situated outside the walls of the chamber and the walls are provided with light transmitting means.

11. Apparatus as claimed in claim 7 in which the illuminating means is situated at the end of the chamber from which the yarn is withdrawn.

12. Apparatus as claimed in claim 11 in which the interior of the chamber is reflecting.

13. Apparatus as claimed in claim 7 in which the illuminating means is situated opposite and across the chamber from the photo-electric cell means.

14. Apparatus as claimed in claim 11 in which the illuminating means is housed in the walls of the chamber.

15. Apparatus as claimed in claim 13 in which the illuminating means is housed in the walls of the chamber.

16. Apparatus as claimed in claim 11 in which the illuminating means projects into the interior of the chamber.

17. Apparatus as claimed in claim 13 in which the illuminating projects into the interior of the chamber.

18. Apparatus as claimed in claim 7 in which the 8 illuminating means is situated outside the walls of the chamber and the walls are provided with light transmitting means.

19. Apparatus as claimed in claim 7 in which the photo-electric cell means comprises a plurality of cells arranged along the chamber, and connected in series to a source of electricity so as to produce a signal substantially smoothly related to the amount of yarn in the chamber.

20. Apparatus as claimed in claim 19 in which each photo-electric cell is shunted with a resistor.

21. Apparatus as claimed in claim 20 in which the photo-electric cell means comprises four cells arranged along the chamber and connected in series.

22. Apparatus as claimed in claim 19 in which a further photo-electric cell is connected across the series of photo-electric cells and situated nearer the crimper than the series of photo-electric cells.

23. Apparatus as claimed in claim 4 in which the related signal is amplified.

24. yApparatus as claimed in claim 4 in which the delivery means and withdrawal means are pairs of driven nip rolls, the drive for the withdrawal means is equipped with a controller and the related signal is fed to said controller.

25. Apparatus as claimed in claim 4 in which the delivery means and advancing means are pairs of driven nip rolls, the drive for the delivery nip rolls is equipped with a controller and the related signal is fed to said controller.

26. Apparatus as claimed in claim 4 in which the stuffer box and the chamber are continuously arranged.

27. Apparatus as claimed in claim 26 in which the staffer box and the chamber are arranged in abutting relationship along a common axis.

References Cited UNITED STATES PATENTS 2,820,988 1/1958 Wegener 28-'72.l4 3,126,431 3/1964 Harder 264-40 3,261,155 7/1966 Kunzle 264-168 X 3,398,224 8/1968 Schatz 264-282 3,417,447 12/1968 Trifunovic 28-72.14 X

ROBERT F. WHITE, Primary Examiner R. R. KUCIA, Assistant Examiner U.S. Cl. XR.

264-168, 282; 18-2 HA; 2li-1.6, 72.14 

